Electrophotographic system

ABSTRACT

An electrostatographic machine in which an opaque original is lit by flashlamps to modulate the reflected light beam which is cast by an optical system onto a moving charged copy sheet so as to leave a latent electrostatic image thereon, which then is developed in a liquid toner bath. The leading edge of the copy sheet moving through the machine triggers the flashlamps. The copy sheet is fed from a magazine to an intermediate station immediately preceding the exposure station where the copy sheet awaits the start of a cycle of operations. At the exposure station, the copy sheet is urged against a glass plane by a repelling charge and by belts.

United States Patent 11113,630,606

[72] Inventor lralVLSage 2,189,001 2/1940 Gould 250/41.5 men/61km. 2,911,944 11/1959 Hayford 118/637 211 AppLNo. 3375x FOREIGN PATENTS [221 Filed 1 901451 7/1962 GreatBritain 1 Patfmmd kc-28,1971 936,221 9/1963 GreatBritain [73] Assignee Pitney Doves-Sage, Inc.

[54] ELECTROPHOTOGRAPHIC SYSTEM 14 Claims, 3 Drawing Figs.

[51] Int. Cl. G03g 15/04 [50] Field oiSurch 95/1.7; 88/24 C; 355/3 [56] References Cited UNITED STATES PATENTS 3,282,177 11/1966 Stanton 95/1.7

3,056,904 10/1962 Kotz 95/77.5

3,076,393 2/1963 Campbell 95/1.7 X

3,241,957 3/1966 Fauser 95/1.7 X

Primary Examiner-John M. Horan Attorneys-William D. Salton, .lr., Albert W. Scribner, Martin D. Willstein and Louis A. Tirelli ABSTRACT: An electrostatographic machine in which an opaque original is lit by flashlamps to modulate the reflected light beam which is cast by an optical system onto a moving charged copy sheet so as to leave a latent electrostatic image thereon, which then is developed in a liquid toner bath. The leading edge of the copy sheet moving through the machine triggers the flashlamps. The copy sheet is fed from a magazine to an intermediate station immediately preceding the exposure station where the copy sheet awaits the start of a cycle of operations. At the exposure station, the copy sheet is urged against a glass plane by a repelling charge and by belts.

ELECTROPHOTOGRAPIIICSYSTEM This invention relates to an electrophotographic system. It is an object of my invention to provide a novel and improved electrophotographic apparatus and method which will reproduce originals accurately, speedily and at a low cost.

It is a more specific object of my invention to provide a riovel and improved apparatus and method of the character described which will make reproductions on photoconductively coated sheets, as distinguished from webs or rolls of photoconductively coated paper.

It is anotherobjectof my invention to provide an electrophotographic apparatus and method which are specially designed to reproduce copies of originals on photoconductively coated sheets in a manner that avoids the need of elaborate scanning arrangements for the originals and the need of synchronizing arrangements for the original and copy sheets such as are presently employedin commercial electrophotographic systems.

I More particularly, it is an object of my invention to provide a novel and improved electrophotographic apparatus and method in which high-speed, high-intensity illumination is employed in photographically transferring the image of a stationary original onto a moving photoconductively coated sheet, such high-speed, high-intensity illumination being secured, in a preferred form of my invention, by the use of a so called strobe, i.e., flash, tube which thus permits the photoconductively coated sheet to betravelling during the time of exposure and yet freezes the paper motion so as to produce a sharp latent image thereon. By enabling the sheet to move while the original is stationary, I am able to avoid expensive scanning and/or synchronizing equipment and methods and yet can obtain a speedy copy output which is as fast as the movement of the copy paper through the system. A system embodyingthe foregoing aspect of my invention can, with simple and inexpensive equipment, produce copy sheets as rapidly as one per second after a short warrnup delay for the first sheet.

It is another object of my invention to provide a system of the character described which, by the use of short-time, highintensity exposure in connection with sequential copy sheets, enables small aperture lenses to be used, thus reducing the need for exact placement of the lens to obtain optimum definition and providing a deeper field of focus, so that wrinkles and ripples in the original will not be out of focus as they would be with a large aperture lens.

Still a further advantage of my system is that by avoiding the use of incandescent illumination I achieve a substantial saving in power and also obviate the accumulation of great quantities of heat which are characteristic of commercial office copy machines. The usual source of light in a standard ofiice copier of the electrophotographic type has an output in the neighborhood of 1,000 watts or more, largely in heat. The very appreciable amount of heat liberated by such sources of light raises the temperature of the entire machine and ultimately affects the operation of the photoconductively coated paper and the liquid or dry toner. By employing a strobe tube, pursuant to my invention, the amount of heat energy released is greatly reduced, thus effecting a savings in consumption of electricity and avoiding the disadvantages consequent upon a significant temperature rise of the machine.

A further advantage of the use of high-intensity, short-term sources of illumination used in accordance with my invention for reproducing originals on coated copy sheets is that strobe, i.e., flash, tubes provide a more even field of illumination and are not plagued by hotspots which characterize incandescent sources of illumination.

It is another object of my invention to form reproductions on coated copy sheets with the use of high-intensity, short-duration illumination that has a spectral distribution which is peculiarly advantageous for copying multicolor originals. More particularly, in this connection, it is an object of my invention to employ xenon-filled tubes, the illumination from which is rich at the blue end of its spectrum. Since all colors absorb blue, the major reflection from a multicolor original thus illuminated will be from the white background. Thereby, the copying systems provides a more uniform reproduction 'of all colors as black or gray.

It is another object of my invention to provide an electrophotographic system which is specially equipped to handle the problems encountered when transporting coated sheets, rather than a web, through a reproducing machine of the character described, so that the sheets will not tend to become so electrostatically attracted to parts of the equipmentthat they will bind in the machine.

Other objects of my invention in part will be obvious and in part will be pointed out hereinafter.

My invention accordingly consists in the features of construction, combinations of elements, arrangements of parts and series of steps which will be exemplified in the apparatus and method hereinafter described and of which the scope of application will be indicated in the appended claims.

In the accompanying drawings in which is shown one of the various possible embodiments of my invention,

FIG. 1 is a side elevational cross-sectional view illustrating the interior of an electrophotographic apparatus made in accordance with my present invention;

FIG. 2 is an electric circuit diagram for said apparatus; and

FIG. 3 is the output spectrum of a xenon-filled flash tube employed in connection with my invention.

Referring now in detail to the drawings, the reference numeral l0 denotes an electrophotographic machine embodying my invention. Said machine includes a housing l2 which is of suitable configuration to enclose and mount the various components of the apparatus which shortly will be described. At the front wall 14 of the housing are situated a group of three manually operable switches 16, 18, 20 which are employed for hold, e.g. toggle, switch (see FIG. 2); the switch 18, which is employed for single copy operation of the machine, is a singlepole, double-throw momentary switch (see FIG. 2); and the switch 20, which is employed for multiple reproduction operation of the machine, is a single-pole, single-throw hold, e.g toggle, switch (see FIG. 2). In addition, there is mounted on the front wall of the housing a pilot lamp 22 (see FIG. 2) to indicate when the machine is ready for operation.

The machine includes suitable means for reception of a fullsize original sheet in a position in which it can be copied. In accordance with my invention said means holds the original sheet stationary, despite the fact, which has been noted previously, that this original sheet will be optically reproduced on a copy sheet that is in transit. The means for placing the original in a predetermined location is situated at any acceptable site on the machine which is convenient for the optical system used for copying. As shown, the receiving means for the original is at the top wall 24 of the housing, and constitutes an aperture 26 of sufficient size to accommodate any original which can be reproduced on the size of copy sheet that is employed, bearing in mind that the optical system may enlarge, reduce or reproduce the same size as the original. Filling the aperture is a pane 28 of glass the upper surface of which is flush with the top of the housing. The glass is suitably held in place, as by a perimetric frame 30.

' Desirably, means also is embodied in the machine 10 to press the original face down flat against the glass pane 28. As illustrated, the pressure means is in the form of a pad constituting a metal plate 32 connected by a parallel double hinge 34 to the top wall 24 of the housing. The undersurface of the metal plate supports a resilient panel 36, e.g., a layer of felt or resilient polyurethane foam, which is designed to press, under the weight of the metal plate, against the back surface of the original on this pane 28. The double hinge 34 permits the level of the plate to be varied when in its operating position against an original.

It is noted that the original may either be a single sheet carrying material to be reproduced, or a book, the housing being sufiiciently large to support the portion of the book opposite to the page being reproduced. The top wall of the housing has been shown short at the front in the illustrated embodiment in order to illustrate the machine to as large a scale as possible. However, in a commercial machine the portion of the top wall forward of the glass pane is made long enough to support the balance of the book, or is sloped down to support the balance of the book when the book is not opened a full 180.

Also included in the housing is a source of high-intensity, short-duration illumination. Such source may, as shown here, constitute several separate units at various locations which are chosen to obtain a substantially uniform field of illumination at the glass pane 28. in the machine illustrated in the drawings 1 have shown two pairs of flash tubes 38, one pair being located below the left-hand front side of the glass pane, and the other pair below the right-hand side of the glass pane. Each pair of flash tubes is backed up by a different trough reflector 40, the reflectors being shaped and tilted to enhance the evenness of illumination at the glass pane. The flash tubes are standard, each including, as is conventional, an elongated cylindrical transparent envelope filled with gas and including electrodes at opposite ends thereof, so as to form a luminous discharge through the gas when the electrodes are energized.

The gas employed preferably is xenon at a suitable pressure. For example, I may use a low-pressure range of from 60 to 200 mm. of mercury or a high-pressure range of from 200 to 400 mm. of mercury. The discharge voltage forthe lower range is in the order of from 60 to 200 volts, while that for the higher range is in the order of from 450 to 2,000 volts.

The specific xenon flash tubes here shown employ xenon at a pressure of 300 mm. In F IG. 3 l have shown the output spectrum of such a xenon flash tube at a current density of 5,300 amp/cm. Attention is directed to the high percentage of energy output at the blue end of thespectrum. As indicated previously, this has the advantage that a large percentage of the luminous energy of thelamps will be absorbed by the full gamut of visible colors, so that where a multicolor original is to be copied, all colors will absorb an appreciable amount of energy and therefore will reproduce well in the electrophotographic copy as dark. This is in contrast to an incandescent source of illumination which, because it contains a high proportion of red and yellow, results in a highly nonuniform absorption by a multicolor copy, sov that with many commercial machines certain colors appear as white due to their reflection rather than absorption.

Although I prefer to utilize a flash tube or tubes as the source of illumination and preferably employ xenon as the gas for the tube, it is within the scope of my invention to utilize less desirable forms of illumination. The prime characteristic of the source of illumination is that it be of high intensity and short duration. This alternatively can be obtained by using an incandescent lamp of high lumen output in conjunction with a high-speed shutter, thereby to obtain, in effect, a short-duration pulse of intense light energy. In such an alternative embodiment the incandescent source of light preferably is turned on shortly before it is required because, due to its high energy output, it would generate too much heat for steady running.

When I have spoken heretofore of short-duration of illumination, I meant a time period in the order of preferably not less than one five-hundredth of a second, for example, from one five-hundredth to one-thousandth of a second, this being sufficient to freeze the motion of a moving copy sheet, hereinafter to be described, with respect to the stationary original disposed on top of the glass pane 28.

The machine further includes an optical system for directly scanning the entire original as a unit and throwing on the copy sheet a beam of light which has been modulated by reflection from the original. The optical system is quite simple.

' it constitutes an adjustable mirror 42 and a lens set 44. The

mirror is positioned on a lower wall 46 of the housing in such orientation as to cast onto the lens set the reflection of the original which it scans. The direction of the optical axis of the scanning and lens system is indicated by the arrows labeled A.

The mirror rests against the inner surface of the inclined lower wall 46, being held in position by any suitable manner as, for instance, by spring bow clips 48 carried by brackets 50. Screws 5! adjust its angular orientation. Both the brackets and the bow clips are out of the optical scanning field and the reflecting field for the mirror 42.

The lens set 44 includes a pair of doublet lenses or any other suitable lens combination which will focus on a copy screen 52 an image of the original on the plate 28. Said copy screen is, of course, perpendicular to the axis of the lens set.

It will be understood by those skilled in the art that the scanning chamber B is, except for the lens set, isolated from the copy chamber C, so that there will be no, extraneous light leakage from the first to the second of these chambers. Hence, the machine includes suitable baffles and walls such as the separating walls 54 and the hood walls 56to effect the foregoing purpose. All internal surfaces of the chamber walls may be formed with a matte black finish to minimize reflection ofv location of any given copy image on a web, and in the elimination of means for obtaining specific spacings between successive copy images on a web. By transporting single discrete sheets, I merely have to feed one sheet at a time to the copying station and then in a'quite simple manner-properly locate the image on that sheet without, however, having to bring the sheet to a halt while the latent electrostatic image is being formed thereon. Thereby, despite the fact that I pass discrete sheets through the machine 1 feed such sheets without halt from a starting position to a finish position through the machine prior to, during and after the formation of a latent electrostatic image on the sheet. Indeed, when the machine is running multiple copies, sheet after sheet flows continuously through the machine from starting to finish position. Thus, I obtain the advantages of a continuous web or set of foldably interconnected sheets without their inherent disadvantages.

The sheets of paper used in my machine are of a conventional type sold on the open market for electrophotographic reproduction. The paper is of any acceptable quality and is characterized by a coating on one surface thereof of a photoconductive layer, that is to say, a layer of material which is of good electrical insulating quality, but which becomes conductive when light impinges thereon. More particularly, where light impinges on any particular spots and areas of such a layer, those spots and areas solely become conductive while the remainder of the sheet maintains its insulating property. A typical photoconductive material is zinc oxide. A typical zinc oxide coated paper is sold by Old Town Corp. of New York City, under the designation Electrofax paper.

The electrophotographic paper used in my machine is in the form of individual sheets which may be cut from a roll in the machine before being fed to the starting position or which, as shown, may be precut and arranged in a stack 58 disposed in a paper compartment 60, Le. magazine, near the top of the machine. Access to the compartment is gained through an aperture 62 in the top wall 24. The aperture is normally closed by a hinged lid 64. To expedite paper pickup, the bottom of the paper compartment is in the form of an upwardly concave wall 66 on which are disposed a series of transverse stationary bars 68 that hold the bottommost sheet in the stack off said wall. Due to the aforesaid configuration of the wall 66 the stack 58 is downwardly bowed, thus facilitating pickoff of the uppermost sheet from the stack.

The pickoff means for withdrawing an uppermost sheet of paper one at a time from said stack constitutes a pickoff roller 70 the opposite ends of which are journaled at the forward free ends of swing levers 72, the rear ends of which are journaled on aligned stationary pins carried by the housing 12. The axes of oscillation of the swing levers and the axis of rotation of the pickoff roller are parallel to the rear, i.e., leading, edges of the sheets of paper in the stack 58. The pickoff roller rests by gravity on the uppermost sheet in the stack near the leading edge thereof.

The pickoff roller is rotated by a sheave 74 integral with an end thereof and about which is trained a belt 76 that is motivated by a drive sheave 78. The drive sheave in tumis powered by the output side of a magnetic clutch 80 the operating coil 82 of which is shown in FIG. 2. The magnetic clutch is idle, i.e., in nondrive condition, when the coil 82 is deenergized, and is rendered operable to transmit power to the sheave 78 when the coil 82 is energized.

Preferably, the axes of oscillation of the swing levers 72 are coincident with the axis of rotation of the drive sheave 78 in order to prevent lengthening or shortening of the belt 76 as the pickoff roller follows the level of the uppermost sheet in the stack 58. However, for purposes of illustration, said oscillating axes of the levers 72 have been shown displaced from the center of rotation of the drive sheave in FIG. 1. It will be apparent, of course, thateven with the indicated locations of said axes of oscillation and axis of rotation, the machine will operate quite satisfactorily providing that the belt 76 is of the stretch type, for instance, is composed of an endless, helically wound resilient wire.

The input side of the magnetic clutch 80 is turned by a geared down drive motor 84 through the medium of a sprocket 85 and a drive chain 86. This chain engages and drives many other components of the machine, but for the moment it is merely necessary to point out that the drive chain 86 engages a sprocket 88 which is gear connected to the input side of the magnetic clutch. Hence, so long as the motor 84 is turning, and this will be at all times that the machine 10 is in operating condition, the input side of the magnetic clutch is being driven. However, as long as the operating coil 82 for the clutch is idle, the output side of the clutch will remain stationary and hence, the pickofi roller 70 will not turn. As soon as the magnetic clutch is energized, the pickoff roller will turn, rotating in such a direction as to advance toward the right (as shown in FIG. 1), i.e., the rear of the machine, the uppermost sheet of paper in the stack 58.

A sheet of paper fed away from its storage position on the stack by the pickoff roller 70 enters the wide mouth of a rearwardly narrowing guide horn 90 and is directed thereby rearwardly and then downwardly to a first feed roller set composed of rollers 92, 94. These two rollers, which preferably are coated with or constitute an elastomeric electrically nonconductive material such asnatural or artificial rubber, form an upwardly facing nip located at the delivery end of the guide hom 90, so that the uppermost sheet of paper leaving the stack 58 will be driven downwardly by the roller set 92, 94.

For a purpose which later will be pointed out, the actuating element 96 of a single-pole, single-throw momentary feather touch (easily actuatable) switch 98 (see also FIG. 2) extends transversely across the guide horn, the guide horn being suitably slotted to permit such location of the actuating element. Hence, the actuating element lies across the path of the leading edge of a sheet of paper passing through the horn. The switch 98 is normally closed so that when the actuating element is not engaged by the leading edge of a sheet of paper,

the contacts of the switch are bridged. However, as soon as the leading edge of a sheet of paper leaving the stack abuts against, so as to depress, the actuating element, the contacts of the switch 98 will be opened. The consequent effect upon the operation of the machine 10 is to idle the magnetic clutch and thereby halt the sheet in a position herein referred to as a starting" position. It will be understood that any equivalent means, e.g., a source of light and a photosensitive cell, can alternatively be employed to sense the aforesaid position of the leading edge of a sheet when it arrives at the starting position.

Immediately below the first feed roller set 92, 94 is a double corona-charging unit 100. The upper end of the unit includes a pair of infeed guiding lips to ensure proper entry of a sheet of paper into the unit, and the lower end of the unit includes a similar pair of outfeed guiding lips. The unit may comprise two opposed structures of very fine parallel wires, such, for example, as are described in U.S. Pat. No. 2,922,883. Said unit 100 is schematically indicated in FIG. 2.

The unit 100 will impose electrostatic charges of opposite polarity to the opposite sides of a sheet of coated paper passing through the same. A suitable charge is '500 to 700 volts. At this time it should be pointed out that the sheets of paper in the stack 58 are arranged with their photoconductively coated sides facing downwardly. Hence, when an in dividual sheet passes through the double corona-charging unit, the photoconductively coated side will be facing in a general direction toward the front of the machine 10. The double corona-charging unit is so electrically connected as to impart a negative electrostatic charge to the front of the sheet and a positive electrostatic charge to the back of the sheet.

Thus, the photoconductive coating has a negative electrostatic charge impressed thereon. This charge will be maintained even after the sheet leaves the charging unit due to the insulating qualities of the photoconductive layer. In the machine 10 the only way that the charge is dissipated locally is either by casting light on spots and areas of the thus charged layer or subsequent to development by touching a ground or exposure to light. A modulated light beam will render the selectively illuminated spots and areas of the coatingelectrically conductive so as to permit discharge thereof and application of toner will partially neutralize the charge of the remaining areas where the toner particles are attracted. However, as the sheet leaves the unit 100, its photoconductive face will be fully and substantially uniformly negatively electrostatically charged, ready to be selectively discharged in a pattern to form a latent electrostatic image in a manner well known to this art.

The first feed roller set 92, 94 is driven by the chain 86. Specifically, the roller 92 is functionally integral with the sprocket 88 while the roller 94 is gear driven from the roller 92 in synchronism therewith, said roller 94 being coincident with the axis of rotation of the magnetic clutch.

A sheet leaving the charging unit 100 is guided by the outfeed lips of the latter to the nip of a second feed roller set constituting the rollers 102, 104. The roller 82 is driven by a sprocket (not shown) which is functionally integral therewith and which engages the chain 86. The rollers 102, 104 are provided with directly interengaging gears, so that when the roller 102 is driven by the chain 86, it, in turn, drives the roller 104 in synchronism therewith. The feed roller set 102, 104 feeds the sheet leaving the unit 100 in a downward direction. The rollers 102, 104 are covered with electrically nonconductive material, e.g., natural or synthetic rubber, so as not to discharge the electrostatic charge on the sheet of coated paper leaving the charging unit. All roller sets that engage the transported sheet of coated paper turn at the same speed.

The back of the copy screen 52 is positioned directly below the outfeed of the roller set 102, 104 and is aligned with the line of contact between said rollers. Thereby, the sheet of paper emerging from between the rollers 102, 104 is fed flatly across the back surface of the copy screen. Desirably, such paper is held fiat against the back of the copy screen so as to minimize optical problems. For this purpose any sort of suitable pressure arrangement may be employed. The one which I have utilized constitutes a transversely spaced series of narrow moving belts 106 formed of an electrically nonconductive material, e.g., natural or synthetic rubber. Each belt has two reaches, one of which contacts the full length of the back of a sheet of paper traversing the back of the screen 52, and the other reach being rearward of the first reach and constituting a return reach. The return reach is maintained under suitable tension by an idler roller 108. The belts are trained about upper and lower rollers. The upper roller constitutes the roller 104. The lower roller constitutes a roller 110. Both rollers 104, 110 are circumferentially grooved in registry to receive the belts 106 and thereby permit the remaining surfaces of said rollers to engage the rear surface of a sheet of paper passing through the machine from starting to finish position. The roller 110 cooperates with a roller 112, the pair constituting an output third feed roller set into the nip of which a sheet of paper leaving the copy screen is directed by the belts 106 and the screen 52. The roller 112 has a functionally integral sprocket (not shown) engaged by the drive chain 86 to turn said roller, and the two rollers 110, 112 have directly intermeshing gears, so that turning of the roller 1 12 will cause the roller 110 to be driven in synchronism therewith; At least one of said rollers is covered with natural or synthetic rubber.

.As of additional assistance in maintaining a sheet of paper flat against the rear surface of the copy screen, I include suitably spaced electrically nonconductive pressure spring fingers 1 14 arranged to press lightly against the back of a sheet of coated paper traversing the back of the screen 52.

There is a tendency for the negatively electrostatically charged front face of a sheet of coated paper passing over the rear surface of the copy screen to stick to said screen due to electrostatic attraction. To counteract this effect, and in accordance with a feature of my invention, I charge the rear surface of the copy screen to a potential of the same polarity as the potential of the electrostatically charged photoconductively coated layer of a sheet of paper in transit through the machine. In the machine being described, the electrostatic charge of the photoconductive layer is negative. Hence, in accordance with the aforesaid feature, the rear surface of the copy screen is negatively coated. Since the copy screen is glass, and, therefore, electrically nonconductive, additional structure must be provided to permit such negative charging. To this end I form on the rear surface of the glass copy screen a transparent electrically conductive coating. Specifically, I utilize a transparent metal, e.g., copper, iron or silver, coating or a transparent coating of an electrically conductive material such as stannous oxide, of a thickness in the order of 1 micron. Such coating has a very substantial light transmissivity, in the order of 90 percent, so that it does not noticeably affect the optical qualities of the machine. The coating of the rear surface of the glass is so thin that it is impractical, even to an enlarged scale, to illustrate it in the same drawing as the glass pane 52. However, said coating, denoted by the reference numetal 116, has been schematically shown in FIG. 2. Any suitable negative charge can be imposed on the coating 116. It is not necessary that it be of the same order of magnitude as the electrostatic charge on the photoconductive coating of a sheet, inasmuch as the mere fact that both charges are of the same polarity will suffice to cause the sheet to be repelled from, or at least not to bind to, the glass pane. For instance, a negative charge in the order of 100 volts on the transparent conductive coating 116 has been found to provide satisfactory results. The circuit for charging the coating is illustrated in FIG. 2 and will be described hereinafter. Said coating is maintained isolated from all conductive parts of the machine 10.

A major feature of my invention is the inclusion in the machine of a sensor which is responsive to the positioning on the copy screen of a complete sheet of electrostatically charged photoconductively coated paper so situated during movement thereof, that the same is ready to have its uniformly electrostatically charged coating selectively discharged by a short-duration high-intensity modulated light beam whereby an electrostatic charge image can be formed thereon. Although the sensor may constitute means sensitive to the location of the trailing edge of a moving coated sheet when said sheet is in a proper position to receive the electrostatic charge image, I prefer not to utilize this arrangement inasmuch as it would entail the use of sequence circuitry. Hence, although a trailing-edge sensing means is within the ambit of my invention, I prefer to employ a sensing means which is responsive to the passage of the leading edge of the sheet of coated paper at the moment when said paper is within the confines of the copy screen in proper position to receive an electrostatic charge image. Hence, the latter position of the sensing means has been shown herein. Any known configuration and structure of sensing means can be employed.

As shown, the aforesaid sensing means comprises a feather touch momentary switch 118 (see also FIG. 2) which experiences a change in condition, e.g., is opened, when the actuating element thereof is encountered by the leading edge of a sheet of coated paper at such time as the sheet is fully on the copy screen, properly positioned to have an electrostatic charge image formed thereon.

The switch 118 may simply constitute an actuating element, such as a feeler, arranged in the path of travel of the sheet of coated paper and near the bottom edge of the copy screen, said actuating element, upon movement, directly opening or closing, depending upon the electrical circuitry, one or more pairs of electric contacts that, when thus moved, will cause the flash tubes 38 to be triggered. However, I have found that when the switch takes on a special form, such as is about to be described, construction and operation of the machine is simplified and improved. The thickness of the coated sheet is quite slight and would not cause an actuating element to move far enough to operate a pair of contacts if a conventional inexpensive commercial momentary switch were employed. In such event, it would be necessary to enlarge the movement of the actuating element caused by the sheet, as for instance, by. having the actuating element extend through the copy screen, so that the moving sheet of paper would have to move the actuating element for a considerable distance, this being sufficient to operate the contacts. However, such movement is prone to buckle the paper and isbetter avoided. The structure which I have employed avoids this difficulty. It also is less expensive than alight switch made up of a source of light and a photosensitive cell. 7

As shown in FIGS. 1 and 2, the electrically conductive movable light spring contact of the momentary switch 118 is biased into engagement with the stationary contact of the switch, the latter being the electrical coating 116 on the rear surface of the glass copy screen 52. Thus, when the paper moves over the coating 116 and under the cantilever spring contact of the switch 118, the spring contact simply is lifted off the coating to break the engagement and open the switch. The spring pressure of the movable contact will restore the engagement once the trailing edge of the sheet of paper has passed. The electric circuitry associated with the switch 118 will be described in connection with the circuit of FIG. 2.

After the sheet has had the electrostatic image pattern formed thereon by a modulated light beam impinging on the charged coating, it is advanced by the third set of feed rollers 110, 112 into and through a developing station which contains a conventional electrophotographic developing liquid in order to convert to visual form the latent electrostatic pattern on the photoconductively coated sheen The developing station includes a developing tank 120 which contains a developing liquid 122. Such liquids are conventional and include finely divided triboelectrostatically charged developer particles dispersed in an electrically insulating liquid. The sheet bearing the latent electrostatic image is transported beneath the surface of a body of the developer liquid. A liquid developer process for latent electrostatic images is described in greater detail by K. A. Metcalf and R. J. Wright, in a paper entitled Xerography,"published in the Journal of the Oil and Color Chemists Association, Nov. I965, Vol. 39, No. l 1, London, England, and in another paper entitled Liquid Developers for Xerography, published in the Journal of Scientific Instruments, Feb. l955, Vol. 32.

Suitable liquid developers are described in US. Pat. Nos. 2,877,l33; 2,890,]74; 2,891,911; 2,899,335; 2,907,674;

3,078,231; and 3,081,263. I

The bottom of the tank 120 is composed of a downwardly bowed perforated pair of parallel guide plates 124 the entrance endbetween which faces the discharge of the third feed roller set 110, 112, so that a sheet of paper leaving said roller set immediately is tracked between these two guide plates. The space between the guide plates is filled with developer liquid which is fed thereto by a pump. Liquid flows into the space through perforations in the top plate and leaves through perforations in the bottom plate from where it drops to a sump 125. Said guide plates are fabricated from an electrically nonconductive material such, for instance, as a plastic, so that they do not discharge the latent electrostatic image on a sheet of paper wherever the paper may touch the same. Hence, a sheet of paper leaving the-roller set 110, 112 will follow a path which brings it below the surface of the liquid developer between the plates 124, so that'normal development may be achieved in a conventional manner.

The exit end of the space between the guide plates leads to the nip between a fourth set of feed rollers 126, 128 which are directly interconnected by gears so that the rollers turn in synchronism. The roller 126 is driven through a functionally integral sprocket (not shown) by the chain 86. The roller sets 126, 'l 28 feed a sheet out from the developing station and also act as squeegees to strip off excess liquid from the front and back surfaces of the now-developed sheet of coated paper rising out of the liquid in the. developing tank. Such excess liquid either falls back into the: space between the guide plates, or falls onto a catchplate l30 beneath the lower roller 128, said catchplate being perforated in the area over the sump 125.

A diverter plate 132 is located above the exit nip of the roller set 126, 128 to direct the forward edge of the developed sheet onto a horizontal conveyor constituting a belt 134 trained about a drive roller 136, an idler roller 138 and a takeup roller 140. A sheave (not shown), functionally integral with the driver roller 136, is connected by a belt 142 to a sheave (not shown), functionally integral with the feedout roller 128, so that the rollers 128, 136 turn in the same direction. Hence, the belt 134 will transfer away from the developer tank a sheet of paper deposited thereon from the diverter plate.

To lift the developer liquid from the sump to the developing tank, I include in conjunction with the developing station, a circulating pump 144 having an intake at the bottom of the sump 125. The outlet 146 of the pump leads to a rising conduit 148 which discharges developer liquid through a spout 150 over the upper perforated guide plate 124 adjacent the entrance to the space between said guide plates, so that freshly turbulent liquid is deposited on the coated surface of the sheet of paper leaving the copy screen almost as soon as the latent electrostatic image has been formed therein.

The conveyor belt 134 leads the still damp developed sheet of paper to a finish position at a drying station composed of stationary guide wires 152 stretched between a pair of shafts 154, so that the sheets of paper bearing the freshly developed images are successively stacked on said wires.

Both at the time of their transport to the wires by the conveyor belt 134 and after assuming their finish position resting on the wires, the freshly developed sheets are subjected to a moving warm stream of air to induce evaporation of the solvent that still remains within the pores and interstices of the sheets.

This is most readily accomplished through the utilization of a fan 156 located in a sleeve 158 across the upper intake end of which is disposed a large number of hot wires resistors 160. Guide wires I62 stretch between shafts 164 which run across the lower discharge end of the sleeve 158 and above the conveyor belt 134, said guide wires 162 serving to prevent the developed sheets of paper on the conveyor belt from curling up too severely and forcing them to follow an appropriate path of travel below the fan without too much fluttering.

Referring now to FIG. 2, in which the electric circuit for the machine 10 is illustrated, it will be seen that a standard AC voltage, as, for example, the M0 to 120 volts AC supply that conventionally is found in plaeesof business, is applied to a pair of mains 166, 168 at least one of which is provided with the usual protective fuse 170. At least one and optionally both mains have a power control switch such, for example, as the off-on switch 16 which constitutes a manually operable singlepole single-throw hold switch which will remain in either (open or closed) position in which it has been last placed. Closure of the switch 16 furnishes power throughout the full length of both mains.

Beyond the switch 16 the various electrical components of my machine are connected across said mains. Thus, the drive motor 84 for the chain 86 has its terminals connected to said mains, as does the motor 172 for the fan 156 and the motor 174 for the circulating pump 144. Hence, as soon as the switch 16 is closed, the fan and pump start their operation and continue it. Also, when the switch 16 is closed, the drive motor 84 starts and continues to turn. Energization of the drive motor actuates the chain 86, whereby so long as the control switch 16 is closed, the chain 86 will be driven and the following sets of feed rollers will continue to turn: the rollers 92, 94 which feed sheets sequentially into the charging unit the rollers 102, 104 which 'arethe outfeed rollers for the charging unit and the infeed rollers for the exposure station; the rollers 110, 112 which are the outfeed rollers for the exposure station and the infeed rollers for the developing station; and the rollers 126, 128 which are the outfeed and liquid-stripping rollers for the developing station. However, the pickoff roller 70 is not necessarily'turned at this time because its operation is dependent upon the state of the magnetic clutch 80, the functioning of which soon will be described; The fan heater resistor wires also are permanently connected across the mains 166, 168.

Additionally permanently connected across the aforesaid mains is the charging unit 100, having high-potential positive and negative terminals 176, 178 which lead to the fine wire grids of said unit.

Further permanently connected across the mains 166, 168 is a photoflash-actuating unit 180, the complete circuit of which is illustrated in FIG. 2, but it is not described in detail because it is entirely conventional. A complete description of said circuit will be found at page 39 of the General Electric Flash Tube Data Manual, No. P5-62P. The values of all of the components of the unit have, for the convenience of .the reader, been set forth alongside of the sundry components. It will be observed that this unit is arranged to actuate the photoflash tubes 38. The unit has a pair of control leads 182, 184 which are connected to a pair of contacts 186. When these contacts are open, the unit stores a charge on the 1,100 mfd. capacitor. Closure of the contacts 186 triggers a discharge of such charge across the electrodes of the flash tubes 38 so as to emit a short-duration, high-intensity pulse of illumination. Where the proper number of tubes are used, as illustrated in FIG. 1, the original to be reproduced is viewed in its entirety by the optical system and thrown onto the copy screen with sufficient brightness to form a latent electrostatic image on the charged coated surface of a sheet then in back of the screen, said image being frozen, despite the unhalted movement of the sheet, because of the short duration of the pulse. The pair of normally closed contacts 186 is controlled by a relay coil 188, the contacts being open when the relay coil is energized. When said coil is deenergized, the contacts 186 will close and the flash tube will be triggered.

Finally, connected across the mains 166, 168 is a control unit 190 for the machine. The control unit includes a full-wave rectifier bridge 192 having a positive output terminal connected to a positive main 194 and a negative output terminal connected to a negative main 196. Direct current is necessary to power the control circuit because a delayed action timing capacitor is employed therein.

The positive main 194 is connected by the single copy" switch 18 to a positive submain 198. Said switch 18, as was noted previously, is a single-pole double-throw switch, and is a momentary switch, that is, it has an idle and an operative position, and will return to its idle position the moment the pressure exerted by manual manipulation thereof is removed.

Hence, said switch preferably is a button-type switch. The movable blade of the switch normally, i.e. when idle (unactuated), is in the position shown in FIG. 2, that is, this blade is in said position when the switch button is not manually depressed. At such time the switch connects the positive main 194 to the submain 198.

The positive submain 198 is connected by the switch 98 to a lead wire 200 which runs to one terminal of the operating coil 82 for the magnetic clutch 80 the opposite terminal of which runs to the negative main 196. The switch 98, as noted previously, is a normally closed, single-pole single-throw momentary switch, the actuating element of which is disposed in the guide horn 90. The normally closed contacts of the switch 98 will open when the leading edge of a sheet of paper depresses the actuating element 96.

The positive submain 198 also is connected by a single-pole double-throw switch 202 to one terminal of a large timing (delayed action) capacitor, e.g., a 60 mfd. condenser 204, the other side of which is connected to the negative main 196. The switch 202, like the switch 186, is controlled by the relay coil 188. The blade of said switch 202 is in the position indicated in FIG. 2 when the coil 188 is energized and said blade swings to the opposite contact when the coil 188 is deenergized. Said opposite contact of the switch 202 is connected by a lead wire 206 to the switch 20 which in turn leads to the lead wire 200. The switch 20 is a "multiple copy" switch which is located on the front wall 14 of the housing and is closed by the operator when multiple copies are desired. Said switch 20 has been shown as being of the toggle switch type to indicate that it is not momentary and can be held closed for any desired length of time. So long as the switch 20 is closed the machine will continue to spew out copies. Said switch may be operated by a counter (not shown) that will cause said switch to open as soon as the desired number of copies has been made.

In the operation of the machine the control switch 16 first is closed to supply power to the various electrical components. Let it be assumed that at this time the machine has first been put into operation, so that all of the paper is in the stack 58, and no sheet is at the starting position. When the'switch 16 is closed, the heater 160 will be energized as will the fan 156 for the heater. Also, the circulating pump will be energized and the drive motor 84 will be in operation. Because the drive motor is turning, the roller sets 92, 94; 102, 104; 110, 112; and 126, 128 will be rotating. However, they will not be driving any paper sheets through the machine. Also, the belts 106 will be moving, but they, too, will not be operating on paper sheets because none is there.

At this time the actuating element 96 of the switch 98 is in its operative position bridging theguide horn 90. Hence, the operating coil 82 for the magnetic clutch 80 will be energized via the following path: the positive main 194; the switch 18, the blade of which is in its idle upper position of P16. 2; the positive submain 198; the switch 98 which at this time is closed; and the lead wire 200. Because the clutch-operating coil 82 is energized, the magnetic clutch 80 will be closed, i.e., will transmit power. Hence, through the belt 76 the sheave 78 associated with the roller 94 will be driving the sheave 74 associated with the pickoff roller 70. Accordingly, the pickoff roller will advance the uppermost sheet in the stack 58, so that its leading edge moves into the guide horn and toward the first feed roller set 92, 94. But before this edge of the sheet can reach the nip of said roller set, it will engage and depress the actuating element 96 causing the switch 98 to open. This removes power from the coil 82 and deenergizes the clutch 80 so as to bring the pickofi roller 70 to a halt. The forward edge of the top sheet thus will come to a rest in a starting position near, but not at, the intake nip of the first feed roller set 92, 94.

While this first sheet is being advanced to the actuating element 96, an alternate circuit parallel to the coil 82 is energized. This circuit is as follows: the positive main 194; the switch 18, with its blade in upper idle position as shown in FIG. 2; the submain 198; the switch 202; a lead wire 208; the

pilot light 22; a current-limiting resistor 210; and the negative main 196. Because the coil 82 is of a low-resistance value, insufficient current flows through the alternate parallel branch to brightly illuminate the pilot lamp. But as soon as the switch 98 opens, the pilot lamp is brightly lit, indicating to the' operator that the machine is ready to be used.

Also, while the coil 82 is energized and even after it is deenergized and the pilot lamp is lit, there is another circuit in parallel with the energizing circuit for the coil 82 and the ac tuating circuit for the lamp 22. This circuit constitutes the delayed action time capacitor 204 which extends between the lead wire 208 and the negative main 196. Said alternate circuit causes the condenser 204 to be charged up both while the lamp 22 is lit and while the coil 82 is energized. The charging circuit remains effective after the switch 98 opens.

If now, with the condenser 204 charged and the switch 98 open, the single copy momentary switch 18 is actuated manually to move its blade from the upper idle contact shown in FIG. 2 to the lower copy contact, the capacitor 204 will be disconnected from its charging circuit and connected through the switches 202 and 18 across the clutch-operating coil 82, causing said coil to be energized for a short period of time. The capacitor is so proportioned that this period is sufficient to cause the magnetic clutch to be closed long enough for the pickoff roller 74 to drive the leading edge of the sheet of paper in the guide horn from its starting position beyond the actuating element 96 to the nip of the first feed roller set 92, 94. The switch 18 is of the slow restoration type, as by having a delay return dashpot connected to its blade so that it will remain closed for a span sufficient to enable the leading edge of the paper to reach the nip of the first set of feed rollers. Shortly thereafter, the coil 82 is deenergized, the capacitor having discharged. But the sheet of paper now will be advanced by the various feed roller sets and belts 104 for the remainder of its travel through the charging station, the exposure station at the copy screen and the developing station to the finish position. The magnetic clutch will open before the trailing edge of the top sheet clears the pickoff roller by discharge of the capacitor 204. It subsequently will reclose on reclosure of the switch 98 to advance the forward edge of the next sheet of coated paper to the actuating element 96.

As the sheet of paper passes through the charging unit 100, it acquires the desired electrostatic charge, particularly the electrostatic charge in its photoconductive front surface which soon will face the copy screen. Upon leaving the charging unit the sheet of paper with its now substantially uniform negative electrostatic charge on its coated face will be driven by the second set of feed rollers 102, 104 and the belts 104 over the back surface of the glass copy screen. Ultimately, the leading edge of this sheet of paper will reach the switch 118. It may be noted at this point, that preferably there are at least two switches 118 disposed in transverse alignment across the copy screen near the lower edge thereof. Said switches are connected in parallel so that both must be operated for proper functioning thereof, plural switches being employed to evenly load the sheet of paper on both sides and thus prevent the paper from cocking which would occasionally take place if only one switch were used.

When both switches 118 are open, the coil l88 is deenergized. Deenergization of said coil causes the triggering contact 186 to close and this will initiate a short-duration, high-intensity pulse of lighting illumination from the flash tubes 38, the duration of the flash being sufficiently short to freeze the motion of the sheet of coated paper which is travelling across the rear surface of the copy screen. Illumination of the picture forms a latent electrostatic image on the previously uniformly charged coated surface of the sheet of paper in the wellknown manner by rendering the illuminated portions of the sheet conductive so at these portions to discharge the electrostatic energy present on the coating. Deenergization of the coil 188 also swings the blade of the switch 202 off its upper contact, thereby opening the charging circuit for the capacitor 204 and the energizing circuit for the pilot lamp 22.

The sheet continues through the developing bath, through the squeegee rollers, over the conveyor, across the fan and onto the stationary guide wires 152 from where it can be removed through an aperture 212 in the front face of the machine.

It will be readily apparent that by the time that the first sheet has cleared the fan, the next sheet will have reached the actuating element 96 and be in a starting position ready for the switch 18 again to be operated, whereby very speedy operation is attained.

When the machine is to be run for multiple copies of the same original, the switch 20 is closed for a long enough time to make the desired number of copies. Closure of the switch 20 sets'up a secondary circuit for alternately energizing the coil 82 from positive main and capacitor 204. It will be noted that the alternate capacitor discharging circuit which is now ready for operation is closed each time the blade of the switch 202 is thrown from its upper contact to its lower contact, this taking place each time that the coil 188 is deenergized. It will be recalled that the coil 188 operates the switch 202, said switch 202 being in its upper position when the coil 188 is energized and in its lower position when the coil 188 is deenergized. The button switch 18 is actuated momentarily to start the multiple cycle.

It thus will be seen that l have provided an apparatus and method which achieve the objects of my invention and which are well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention and as various changes might be made in the embodiment above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. An electrophotographic apparatus comprising A. means for supplying copy sheets each having a photoconductive surface,

B. a charging station,

C. a reproduction station including i. a transparent support D. a developing station,

E. means for placement in a predetermined position of an original to be copied,

F. an optical system situated to throw an image of the original on the transparent support,

G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position,

i. wherein the starting position of a copy sheet is a position in which the leading edge of the copy sheet is between the location of said leading edge while in the sheet supply means and the location of said leading edge shortly before the charging station, said copy sheet being stationary in said starting position,

H. means to move said leading edge of the sheet to the charging station after which the transporting means moves the copy sheet to the finish position,

. sensing means actuated upon the location in a certain position of the leading edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system,

J. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its aforesaid predetermined position, and

K. means operable upon actuation of the sensing means by said edge of the moving copy sheet to render said source of illumination effective,

L. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the charging station so as to produce thereon a latent electrostatic image which subsequently is rendered visible at the developing station.

2. An electrophotographic apparatus comprising A. means for supplying copy sheets each having a photoconductive surface,

B. a charging station,

C. a reproduction station including i. a transparent support D. a developing station,

E. means for placement in a predetermined position of an original to be copied,

F. an optical system situated to throw an image of the original on the transparent support,

G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position,

H. means to move a copy sheet at the sheet supply means from said supply means to the starting position at which said sheet comes to rest, a

l. means to render said transporting means effective to move said sheet to the charging station after which the transporting means moves the sheet to the finish position,

J. sensing means actuated upon the location in a certain position of an edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system,

K. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its aforesaid predetermined position, and

L. means operable upon actuation of the sensing means by said edge of the moving copy sheet to render said source of illumination effective,

M. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the chargingstation so as to produce thereon a latent electrostatic image which substantially is rendered visible at the developing station.

3. An electrophotographic apparatus comprising A. means for supplying copy sheets each having a photoconductive surface,

B. a charging station,

C. a reproduction station including i. a transparent support,

D. a developing station,

E. means for placement in a predetermined position of an original to be copied,

F. an optical system situated to throw an image of the original on the transparent support,

G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position,

H. means to move a copy sheet at the sheet supply means from said supply means toward the charging station,

I. first sensing means responsive to the position of said sheet to stop the sheet at the starting position short of the charging station,

J. means to start the sheet moving again from the starting position to the charging station after which the transporting means moves the sheet to the finish position,

K. second sensing means actuated upon the location in a certain position of an edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system,

L. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its aforesaid predetermined position, and

M. means operable upon actuation of the second sensing means by said edge of the moving copy sheet to render said source of illumination 'eflective,

N. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the charging station so as to produce thereon a latent electrostatic image which subsequently is rendered visible at the developing station.

4. An electrophotographic apparatus comprising A. means for supplying copy sheets each having aphotoconductive sprface,

B. a charging station,

C. a reproduction station including i. a transparent support D. a developing station,

E. means for placement in a predetermined position of an original to be copied,

F. an optical system situated to throw an image of the original on the transparent support,

G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position, v

H. sensing means actuated upon the location in a certain position of an edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system,

. means to electrostatically repel the photoconductive surface of the copy sheet from the transparent support as the sheet is in transit through the reproduction station,

J. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its 'aforesaid predetermined position, and

K. means operable upon actuation of the sensing means by said edge of the moving copy sheet to render said source of illumination effective,

L. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the charging station so as to produce thereon a latent electrostatic image which subsequently is rendered visible at the developing station.

5. An apparatus as set forth in claim 4 wherein the transparent support is an electrically nonconductive member, and wherein the repelling means includes a transparent electrically conductive coating disposed on the surface of said member across which the copy sheet passes, and means to charge said electrically conductive transparent coating to the same polarity as the electrostatic charge on the photoconductive surface on the copy sheet.

6. An apparatus as set forth in claim 5 wherein the transparent electrically conductive coating is a thin film of metal.

7. An apparatus as set forth in claim 5 wherein the transparent electrically conductive coatingis a thin film of stannous oxide,

8. An apparatus as set forth in claim 5 wherein the sensing means includes a switch, one contact of which is the electrically conductive coating on the transparent support and the other contact of which is an electrically conductive element biased into engagement with said coating, so that the switch will be actuated by passage of the mentioned edge of the copy sheet between the contacts thereof.

9. An electrophotographic apparatus comprising a flexible member having a photoconductive surface, a charging station, a reproduction station including a guide element, means to move the flexible member through the charging station where the photoconductive surface has an electrostatic charge of a given polarity impressed thereon and through the reproducron station where the electrostatically charged photoconductive surface of the member contacts the guide element and receives a light image that impresses a latent electrostatic charge image thereon, and means to repel the flexible member from the guide element, said repelling means including means I to impress on the surface of the guide element in contact with the electrostatically charged photoconductive surface of the flexible member a charge of a polarity the same as the electrostatic charge on said photoconductive surface.

10. An apparatus as set forth in claim 9 wherein the guide element is an electrically nonconductive transparent support, and wherein the repelling means includes an electrically conductive thin coating on the surface of the screen contacted by the flexible member, which coating has the repelling charge impressed thereon.

II. An apparatus as set forth in claim 10 wherein the electrically conductive coating and the transparent support are transparent.

12. An apparatus as set forth in claim 11 wherein the electrically conductive coating is'composed of stannous oxide.

13. An apparatus as set forth in claim ll wherein the electrically conductive coating is metal.

14. An apparatus as set forth in claim ll wherein the flexible member is electrically nonconductive between its front and back surfaces andwherein a sensing means is associated with the transparent support, said sensing means constituting a switch, one contact of which is the thin coating, and the other contact of which is an electrically conductive member biased into engagement with said coating, whereby the switch is actuated by introduction of the flexible member passing over the coating between said contacts, said sensing means being connected in a circuit with a light source arranged to illuminate an opaque original when the sensing means is actuated so as to cast onto the photoconductive surface at the reproduction station a reflection of a light beam modulated by the opaque original. 

1. An electrophotographic apparatus comprising A. means for supplying copy sheets each having a photoconductive surface, B. a charging station, C. a reproduction station including i. a transparent support D. a develOping station, E. means for placement in a predetermined position of an original to be copied, F. an optical system situated to throw an image of the original on the transparent support, G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position, i. wherein the starting position of a copy sheet is a position in which the leading edge of the copy sheet is between the location of said leading edge while in the sheet supply means and the location of said leading edge shortly before the charging station, said copy sheet being stationary in said starting position, H. means to move said leading edge of the sheet to the charging station after which the transporting means moves the copy sheet to the finish position, I. sensing means actuated upon the location in a certain position of the leading edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system, J. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its aforesaid predetermined position, and K. means operable upon actuation of the sensing means by said edge of the moving copy sheet to render said source of illumination effective, L. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the charging station so as to produce thereon a latent electrostatic image which subsequently is rendered visible at the developing station.
 2. An electrophotographic apparatus comprising A. means for supplying copy sheets each having a photoconductive surface, B. a charging station, C. a reproduction station including i. a transparent support D. a developing station, E. means for placement in a predetermined position of an original to be copied, F. an optical system situated to throw an image of the original on the transparent support, G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position, H. means to move a copy sheet at the sheet supply means from said supply means to the starting position at which said sheet comes to rest, I. means to render said transporting means effective to move said sheet to the charging station after which the transporting means moves the sheet to the finish position, J. sensing means actuated upon the location in a certain position of an edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system, K. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its aforesaid predetermined position, and L. means operable upon actuation of the sensing means by said edge of the moving copy sheet to render said source of illumination effective, M. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the charging station so as to produce thereon a latent electrostatic image which substantially is rendered visible at the developing station.
 3. An electrophotographic apparatus comprising A. means for supplying copy sheets each having a photoconductive surface, B. a charging station, C. a reproduction station including i. a transparent sUpport, D. a developing station, E. means for placement in a predetermined position of an original to be copied, F. an optical system situated to throw an image of the original on the transparent support, G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position, H. means to move a copy sheet at the sheet supply means from said supply means toward the charging station, I. first sensing means responsive to the position of said sheet to stop the sheet at the starting position short of the charging station, J. means to start the sheet moving again from the starting position to the charging station after which the transporting means moves the sheet to the finish position, K. second sensing means actuated upon the location in a certain position of an edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system, L. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its aforesaid predetermined position, and M. means operable upon actuation of the second sensing means by said edge of the moving copy sheet to render said source of illumination effective, N. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the charging station so as to produce thereon a latent electrostatic image which subsequently is rendered visible at the developing station.
 4. An electrophotographic apparatus comprising A. means for supplying copy sheets each having a photoconductive surface, B. a charging station, C. a reproduction station including i. a transparent support D. a developing station, E. means for placement in a predetermined position of an original to be copied, F. an optical system situated to throw an image of the original on the transparent support, G. means to transport a single copy sheet without stop from a starting position through the charging station, reproduction station and developing station to a finish position, H. sensing means actuated upon the location in a certain position of an edge of the copy sheet perpendicular to its direction of transportation while the copy sheet is in transit across the transparent support, said position being such that the copy sheet is within the confines of the transparent support properly situated to receive the entire image of the original cast thereon by the optical system, I. means to electrostatically repel the photoconductive surface of the copy sheet from the transparent support as the sheet is in transit through the reproduction station, J. a high-intensity, short-duration source of illumination arranged to illuminate the entire original in its aforesaid predetermined position, and K. means operable upon actuation of the sensing means by said edge of the moving copy sheet to render said source of illumination effective, L. whereby to freeze movement of the copy sheet and vary the electrostatic charge imposed on the photoconductive surface thereof at the charging station so as to produce thereon a latent electrostatic image which subsequently is rendered visible at the developing station.
 5. An apparatus as set forth in claim 4 wherein the transparent support is an electrically nonconductive member, and wherein the repelling means includes a transparent electrically conductive coating disposed on the surface of said member across which the copy sheet passes, and means to charge said electrically conductive transparent coating to the same polarity as the electrostaTic charge on the photoconductive surface on the copy sheet.
 6. An apparatus as set forth in claim 5 wherein the transparent electrically conductive coating is a thin film of metal.
 7. An apparatus as set forth in claim 5 wherein the transparent electrically conductive coating is a thin film of stannous oxide.
 8. An apparatus as set forth in claim 5 wherein the sensing means includes a switch, one contact of which is the electrically conductive coating on the transparent support and the other contact of which is an electrically conductive element biased into engagement with said coating, so that the switch will be actuated by passage of the mentioned edge of the copy sheet between the contacts thereof.
 9. An electrophotographic apparatus comprising a flexible member having a photoconductive surface, a charging station, a reproduction station including a guide element, means to move the flexible member through the charging station where the photoconductive surface has an electrostatic charge of a given polarity impressed thereon and through the reproduction station where the electrostatically charged photoconductive surface of the member contacts the guide element and receives a light image that impresses a latent electrostatic charge image thereon, and means to repel the flexible member from the guide element, said repelling means including means to impress on the surface of the guide element in contact with the electrostatically charged photoconductive surface of the flexible member a charge of a polarity the same as the electrostatic charge on said photoconductive surface.
 10. An apparatus as set forth in claim 9 wherein the guide element is an electrically nonconductive transparent support, and wherein the repelling means includes an electrically conductive thin coating on the surface of the screen contacted by the flexible member, which coating has the repelling charge impressed thereon.
 11. An apparatus as set forth in claim 10 wherein the electrically conductive coating and the transparent support are transparent.
 12. An apparatus as set forth in claim 11 wherein the electrically conductive coating is composed of stannous oxide.
 13. An apparatus as set forth in claim 11 wherein the electrically conductive coating is metal.
 14. An apparatus as set forth in claim 11 wherein the flexible member is electrically nonconductive between its front and back surfaces and wherein a sensing means is associated with the transparent support, said sensing means constituting a switch, one contact of which is the thin coating, and the other contact of which is an electrically conductive member biased into engagement with said coating, whereby the switch is actuated by introduction of the flexible member passing over the coating between said contacts, said sensing means being connected in a circuit with a light source arranged to illuminate an opaque original when the sensing means is actuated so as to cast onto the photoconductive surface at the reproduction station a reflection of a light beam modulated by the opaque original. 